This invention relates to an engine stop control device and more particularly to improved method and apparatus for stopping a direct cylinder injected internal combustion engine.
The advantages of utilizing direct cylinder fuel injection for providing fuel economy and also more effective exhaust emission control are well known. However, direct cylinder fuel injection presents certain difficulties.
Specifically, since the fuel injector is positioned directly in the combustion chamber, it must be designed so as to withstand extremely high temperatures caused by the burning of the fuel in the combustion chamber. In addition, the fuel injector, which normally employs an injection valve that opens and closes to control the admission of fuel into the cylinder, can be prone to malfunctioning if deposits are formed on the valving surfaces or within the interior of the injector.
One particular condition when damage can occur to the fuel injector is when the engine is shut off. If the engine is switched off at a time when the injector valve is opened, there is a possibility that the spark plug may still fire and thus the combustion which will occur in the chamber occurs when the injector valve is opened. This can readily promote damage to the interior of the injector and the formation of carbon or other deposits either on the injector valve seating surfaces or within the body of the injector that can cause running difficulties when the engine is re-started.
This particular problem can be understood by reference to FIGS. 1 and 2 which are respectively, the timing diagram for a single cylinder of a two stroke, direct air/fuel injected internal combustion engine and a time diagram showing the condition of the passage of current through the spark coils and the kill switch of the engine.
Referring first to FIG. 1, this figure shows the timing conditions for a single cylinder of a two cylinder, two cycle, crankcase compression, internal combustion engine. Although the invention is described in conjunction with two stroke engines and engines having two cylinders, it should be readily apparent to those skilled in the art that the invention may be employed with four cycle direct cylinder injected engines and/or engine having any number of cylinders and any cylinder configuration. In fact, the invention also may be utilized in conjunction with rotary engines and the term "cylinder" as used in the specification and claims is intended to cover the combustion chamber regardless of how it is formed. The invention, however, has particular utility with two stroke or ported type rotary engines since they are more prone to the type of problem because of the overlap of the port opening and injection timing.
Referring now to FIG. 1, it will be seen that as the crankshaft rotates approximately past the 90.degree. point, the exhaust port will open and after approximately 120.degree. of rotation, the scavenge port will open. The scavenge port closes sometime at approximately 240.degree. after top dead center and the exhaust port closes slightly before 270.degree. after top dead center.
The timing diagram illustrates the condition for a fuel/air injector and one of the pre-charged type wherein fuel injection begins at approximately top dead center and continues into the injector chamber until about 150.degree. after top dead center. At this time, the air pressure in the chamber of the air/fuel injector is maintained low and once fuel injection is completed, then the chamber is further pressurized with air. At approximately 190.degree. after top dead center, the injector valve opens to permit the air and fuel to issue into the combustion chamber and the injector valve closes at approximately 270.degree. after top dead center. The spark plug is fired at sometime before top dead center and after the injector valve has been closed in normal low speed, low load engine running.
The timing for the remaining cylinder is the same as that of the cylinder shown in FIG. 1 but in the actual engine, of course, the cylinders will fire at different times normally.
When the speed and load of the engine is higher than idle, the time of fuel injection is increased by the fuel injector and also the duration of opening of the injection valve is extended so that there will be some overlap between the time when the fuel injection valve is opened and the spark plug begins to fire. This presents a problem when shutting off the engine, because the mere initiated of the kill switch operation does not immediately stop the firing of the spark plugs as may be seen from FIG. 2 which shows the timing for both cylinders and the condition of the kill or ignition switch.
The top curves show the condition of the primary windings of the spark coils associated with the individual spark plugs and the next two curves show the firing condition of the associated spark plugs. It should be noted that the spark plug firing lags slightly the current flow through the primary winding of the spark coils so that the spark plugs fire slightly after current begins to flow through the primary winding of the coils and continues for a brief period of time after the primary winding is de-energized, as is well known.
Assuming the kill switch is turned off sometime t.sub.2 after the spark plug associated with the number one cylinder has begun fire t.sub.1, the spark plug firing will continue for a time period up until the time period t.sub.3 due to the fact that there is this lag between the de-energization of the primary winding and the actual shutting off of the engine. Because of the fact that the spark is still firing and the fuel injection valve may be opened, then obviously damage can occur to the fuel injector and at the minimum, there will be combustion chamber deposits form in the chamber of the fuel injector which can cause the fuel injector to malfunction with the engine is next started.
It is, therefore, a principle object to this invention to provide an improved control for the stopping of an engine which insures that the spark plug firing will be discontinued only after it is insured that the actuating signal for the injection valve has been turned off.
It is a further object to this invention to provide an interrelated control for the injector valve and ignition circuit of an engine that insures that the injector valve is deactivated before firing of the spark plugs is terminated.